1. Field of the Invention
The invention is in the field of wireless communication inside buildings, and in particular deals with carrying wireless communication over wiring infrastructure used for Ethernet.
2. Description of Related Art
The invention relates to an In Building (IB) communication system for propagating wireless signals inside buildings using existing wiring infrastructure carrying Ethernet signals.
Several systems and application exist today where cellular or other high frequency signals are propagated through copper wires such as telephone or Ethernet wiring. Since the bandwidth of copper wires is limited, high frequency signals in the frequency bandwidths of cellular communication are not able to propagate through the copper wires without significant attenuation.
In the prior art, illustrated in FIG. 1, the incoming high frequency signal at frequency band F1 is mixed by mixer 104 with the signal of a local oscillator 106 having a frequency f2. The product of the mixer includes several signals at frequency band F3 described by F3=±F1±f2. A filter 108 at the output of the mixer 104 selects specific frequency band F3 out of the several possible combinations, for example: F3=f2−F1. The signals within this frequency band are fed to the copper wires 109 and arrives through it to the remote unit which includes a mixer 112, a local oscillator 114 and a band pass filter 118. The incoming signals at frequency band F3 are mixed at mixer 112 with a signal at frequency f5 produced by local oscillator 114. Filter 118 at the output of mixer 112 selects the required frequency band: F6=f5−F3. In order for signals in F6 to be an accurate replica of signals in F1, f5 needs to be exactly the same frequency as f2. Namely, local oscillators 106 and 114 should be locked to the same frequency. To this aim, a reference signal feeds the local oscillator at the Hub unit, and its signal is transferred to the local oscillator at the remote unit for locking it to the same frequency. In the example of FIG. 1, a reference generator 120 located on the hub unit synchronizes local oscillator 106 of the hub unit. A dedicated resource such as physical cable 122 or dedicated bandwidth in cable 109 is used for transferring the reference signal from the reference generator 120 in the hub unit to the remote unit. U.S. Pat. No. 6,157,810 to Georges proposes to transfer between the hub unit and the remote unit a “reference tone” in a “intermediate frequency”, which is low enough to be transferred through copper wires.
The approach of the prior art where a special bandwidth is dedicated to the reference signal requires a dedicated special frequency band in the limited bandwidth of the wires and also requires use of a relatively expensive hardware such as sharp band pass filter, mixer in order to filter the reference signal out of the other signals. Moreover, the transfer of reference signal through the cables creates additional interference that might block or degrade other communication channels.
In such systems the hub unit and the remote unit exchange management data that includes indications on the status and operation conditions of electronic circuits in the remote units. This data is generated in the remote units and sent to the hub unit. Management data may also include control messages sent from the hub unit to the remote units for controlling their circuits. Also, other synchronization signals such as a signal synchronizing the receive/transmit state of TDD (Time Division Duplexing) repeaters, need to transferred between the hub unit and the remote unit.
In order to save bandwidth, electronic components and circuits and avoid the need for a dedicated frequency band for the reference signals, management and other data and synchronization signals, it is an objective of the current invention to combine the reference signals, the additional data and the other synchronization signals with a asynchronous Ethernet signal and generate a single synchronized unified data stream used to convey all required signals and synchronize the local oscillators at both sides of the wiring.